What is the most reliable .40? Hard to say since every .40 I've known personally has been extremely reliable.
I used to own a CZ 40B. I sold it a few years ago and I had it about a year before that so my memory might not be completely fresh, but I don't remember it ever failing. I do remember that I considered it very reliable, even a bit more than my CZ 75B. I don't remember any hiccup and if it had one it was maybe one or two minor hiccups during break-in. I don't know what kind of luck the current owner, Spot77, has had.
I currently own a Taurus PT140 Milennium Pro. I have 640 rounds, almost half of them a variety of JHPs, and it has never had a gun related failure (one factory load that the round pretty much self-destructed, but no gun related failures).
I am currently betting the price of a used gun that the SIG 229 will be the same as I recently bought one online and should have it in my hands in a month (MD law requires I wait a month since I just took delivery of a gun today).
I don't know if it has anything to do with the chambering but I've had far fewer problems combined out of the two .40s I've owned than any one of my other auto calibers (a weird dry fire issue with my Bersa .380 when brand new that resolved itself, one or two minor issues with my Ruger KP345 before learning it doesn't like to be dry, a couple bobbles with my 1911, and a handful of minor bobbles with my 9mm CZ 75B). Hmm, lets see how my new (to me) 9mm SIG 226 and new (to me) .40S&W SIG 229 fare.